The figure shows a section of a renal glomerulus. The glomerulus is a ball of capillary loops that are surrounded by the blind end of the renal tubule called Bowman’s capsule. Between the loops are cells called mesangial cells which together with the surrounding matrix form the mesangium. The mesangium is mesenchymal in origin and contains myofilaments that resemble smooth muscle in structure. The contractile nature and location of the mesangium permits it to function as a regulator of glomerular filtration by altering the capillary surface area available for filtration. Mesangial cells are also known to take up immune complexes.